I. Field of the Invention
This invention relates generally to instruments for facilitating the placement of electrical stimulating/sensing leads in the body of a patient and more particularly to an improved device for the affixation of a sutureless electrode on such a lead to cardiac tissue.
II. Discussion of the Prior Art
Medical electrode placement directly upon or within myocardial (heart) tissue is commonplace, and many medical electrode placement systems have been devised to assist in attaining accurate placement. However, as will be set forth in greater detail below, these systems share a common problem. Many of them utilize the principle of grasping an insulating head from which the electrode projects with an introducer, positioning the electrode appropriately, then releasing the head and withdrawing the tool. The problem is that the relatively bulky head remains. Other lead designs utilize an internal clamping mechanism to avoid this problem, but they still have other bulky projections on their surface.
A typical prior art cardiac stimulating lead comprises an elongated lead body having a proximal and distal end. The lead body includes one or more flexible electrical conductors contained within a pliable, flexible insulating sheath. Suitable connectors are affixed to the proximal end of the conductors for facilitating attachment to an implantable or external electrical stimulating pulse generator. Affixed to the distal end of the lead body are one or more electrodes which are joined to the embedded conductor(s).
One known type of stimulating lead is the so-called myocardial screw-in lead. In this arrangement, one of the electrodes comprises a rigid helix having spaced-apart convolutions. It is supported by a molded plastic head, with the helix projecting perpendicularly from a surface of the head. The lead is installed using a specially designed tool which frictionally grasps the lead head, allowing the helix to be rotated into and be anchored by the tissue to be stimulated. Thus, the tool is used much like a screw driver. The head from which the electrode protrudes often includes irregular protuberances with which the insertion tool is intended to cooperate. This irregular surface may rub against tissue. Eventually, the rubbing can create severe medical problems for the patient, examples of which are common in the medical literature. These involve both sutured and sutureless electrodes.
The present invention obviates the need to avoid electrodes that have extensions or other protrusions on their upper surface. Unfortunately, prior art approaches to the releasible introduction of myocardial electrodes have relied either upon grasping such extensions or protrusions, or upon dimensioning the electrode to permit internal grasping, requiring a bulky electrode head.
An example of an electrode that requires a forceps-like device for insertion is disclosed in U.S. Pat. No. 4,144,890 of Hess. Forceps are used to flex the electrode body into a concave posture. The surface prongs are inserted into the myocardium, then the forceps are released. Distension of the electrode body firmly anchors the surface prongs within the tissue. Necessarily, then, the electrode head must be dimensioned to receive the forceps, which results in a potentially abrasive shape.
A lead installation tool utilizing a releasable clamp that mates with an electrode mounting head is disclosed in U.S. Pat. No. 4,271,846 of Little. A specially-designed electrode head has a groove into which an abutment fits until the corkscrew electrode is properly placed in the myocardium. A clamp operator conductor carrier assembly then moves the clamp into a release position, and the installation tool can then be removed from the field. Although the upper edge of this electrode is rounded, the edges defined by the groove may rub against tissue such as the atrial appendage, causing damage.
An alternative introducer tool is disclosed in U.S. Pat. No. 4,646,755 of Kane. Using an insertable stylet that is fed through the lumen of an electrode lead, this tool includes a plunger housing. The plunger housing shifts within a locking tube to engage the tool in an advanced or a retracted position. When in the advanced position, clamping elements on this plunger housing engage the stylet to prevent movement. Thereupon, the lead may be rotated about the stylet in relation to the introducer tool in order to affix the helical attachment assembly on the electrode surface within tissue.
It is accordingly a principal object of the present invention to provide a new and improved apparatus for affixing sutureless myocardial leads to cardiac tissue.
It is another object to permit the use of lead head that is smoother, rounded and void of sharply edged surfaces and thus less irritating to tissue, particularly in pediatric patients.
Another object is to avoid erosion through surrounding tissues due to lead irritation.